Shielded waveguide window



July 15, 1958 R. J. BONDLEY ET AL 2,843,795

SHIELDED WAVEGUIDE WINDOW Filed June 9, 1954 ['2 ventor's [fa/p/z J. Bone leg 5 Rudovh A. De/m by Q/ 4 73cm f zezkAttorney.

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SHIELDED WAVEGUIDE WINDOW Ralph J. Bondley, Scotia, and Rudolph A. Dehn, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application June 9, 1954, Serial No. 435,476

3 Claims. (Cl. 315-539) Our invention relates to a method and apparatus for eliminating electrical and mechanical failure of windows used to hermetically seal the portion of an apparatus utilized for generating high power electromagnetic energy.

In the building of vacuum tubes for the generation of high power energy at microwave frequencies, one problem is that of providing a means of extracting the energy from the generator and coupling it to a suitable trans mission line or waveguide. It is common practice to use a hermetically sealed dielectric window to couple radio frequency energy to a waveguide and to separate the vacuum portion of the tube from the waveguide, which is customarily maintained at atmospheric or higher pressure. At high power levels, electrical and mechanical failure of the window often occurs. In cases where this failure rate has been excessive, the window has been in a direct line 'of sight with the electron stream used in generating the microwave energy.

It is therefore an object of our invention to provide an improved apparatus and method for coupling to the portion of an apparatus utilized for generating high power electromagnetic energy.

It is also an object of our invention to provide a method and apparatus for preventing the breakdown of hermetically sealed dielectric windows.

Another object of our invention is to provide an improved apparatus and method for coupling to the vacuum portion of a microwave tube wherein the pressure isolating window is shielded from the electron stream generating the microwave energy.

A further object of our invention is to provide amethod and apparatus for coupling it to a microwave tube wherein the pressure isolating window is located out of a direct line of sight from and shielded from the electron stream generating the microwave energy.

Our invention provides for shielding a dielectric window from an electron stream and a specific embodiment thereof utilizes a section of waveguide which is bent at an angle so that one end of the waveguide may be coupled to an aperture in a resonant cavity of a microwave tube such as a klystron. A dielectric window is hermetically sealed across the other end of the waveguide. The dielectric window is out of the direct line of sight from the electron stream in the microwave tube. Further shielding is provided by placing a lead shield partially around the resonant cavity and partially around a portion of the waveguide to shield the dielectric window from stray X-radiation generated by the stream of electrons. I

A better understanding of our invention may be had by referring to the figures of the drawing which illustrate, by way of an example, an embodiment of our invention. Figure 1 illustrates a sectional view of a portion of a microwave tube apparatus looking along section 11 of Figure 2; Figure 2 is a further illustration of the apparatus shown in Figure 1 taken along section 22 of Figure l; and Figure 3 illustrates another view of the atent O 2,843,795 Patented July 15, 1958 apparatus of Figure 1 taken along section line 33 of Figure 2.

It is noted that the apparatus of our invention is adapted to but not limited to microwave apparatus operating at a frequency of approximately 1,000 megacycles. Such microwave apparatus may be a high power klystron having electrons in the electron stream with energies ranging from 200,000 to 350,000 electron volts. Electrons having energies in this range generate X-rays when they strike certain materials such as copper or copper alloys which are customarily used in the construction of microwave apparatus. These X-rays and stray high energy electrons are a cause of dielectric window failure in microwave equipments operating at high power levels.

Figures 1 to 3 illustrate a portion of a microwave tube such as a high power klystron in which the energy on tracting apparatus consists generally of resonant cavity 1 and waveguide section 4 hermetically sealed by dielectric window 9. Other portions of a microwave system which operate at pressures other than the pressure within resonant cavity 1 may be coupled to waveguide section 4. An electron stream from a source of electrons, such as a thermionic cathode, enters resonant cavity 1 through copper tube 2. The electron stream continues through cavity 1 and into collector 3, the top end of which appears in Figures 1 and 2 of the drawing. This stream of electrons contains bunches of electrons which, when passing through resonant cavity 1, excite the cavity at the frequency to which it is tuned. Waveguide section 4 is mechanically and electrically coupled to resonant cavity 1 so that electrical energy, at the frequency to which resonant cavity 1 is tuned, is coupled through tuned aperture 5 into waveguide section 4. The waveguide section 4 consists of sections 6 and 7. Section 7 is tapered to match the impedance of resonant cavity 1 to the impedance of a waveguide system (not shown). The end of waveguide 4 is provided with a copper flange 8 to which dielectric window 9 is hermetically sealed. Dielectric window 9 is suitably secured to flange 8 by means of metal members 10 and 11. A preferred form of waveguide window which may be used in this apparatus is completely described and is claimed in a patent application by Ralph J. Bondley, Serial No. 403,597, filed January 12, 1954, and assigned to the same assignee as this application. Bolt holes 12 are provided for coupling the waveguide section 4 and flange 8 to other portions of a waveguide system. The waveguide window 9 is designed to provide electromagnetic coupling between waveguide section 4 and subsequent waveguide sections while maintaining a hermetic seal between the interior of cavity 1 and attached waveguide sections.

Waveguide 4 is formed with a ninety degree bend so that waveguide window 9 is located out of the direct line of sight from the electron stream passing from tube 2, through resonant cavity 1 and into collector 3. Therefore, the window is shielded from the electron stream of the microwave power generator and the tendency to build up charge on the window due to bombardment by stray electrons is reduced. As has been previously noted electrons having high energies produce X-rays when they strike certain materials customarily used in vacuum tube construction. In order to prevent X-ray bombardment of the dielectric window a heavy shield 13 of X-ray absorbent material such as lead is provided which partially surrounds resonant cavity 1. Further shielding is provided for the window by means of thin lead shield 14 which covers three sides of the rectangular waveguide 4. Lead shield 13 also provides protection for personnel working in the immediate vicinity of this microwave power generator. The combined eflfect of proper orientation of the window and the lead shielding results in a reduced tendency for such windows to fail due to the 3 build up of charge on the window as well as the deteriorating effects of X-radiation on the dielectric and dielectric-to-metal seals.

It may be seen from the foregoing description that we provide a novel method and apparatus for extracting high power electromagnetic energy at microwave frequencies from a portion of a microwave tube and coupling it to a Waveguide section operating at a different pressure.

the window from the electron stream.

It will be appreciated by those skilled in the art that the above-described embodiment of our invention is given merely by way of example. Therefore, we intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for interaction with an electron beam and the transmission of high frequency electromagnetic energy comprising a chamber having spaced-opposed Walls provided with aligned apertures for the passage of an electron beam, a wall connecting said opposed walls and having an aperture therein for the passage of electromagnetic wave energy, a waveguide coupled to said chamber and having an axis extending in a direction perpendicular to the direction of an electron beam passing through the aligned apertures in said spaced opposed walls, and a dielectric window hermetically sealed to said waveguide and shielded by means of a wall of said waveguide from straight line exposure to an electron beam passing through said aligned apertures.

2. Apparatus for interaction with an electron beam and the transmission of high frequency electromagnetic energy comprising a chamber having spaced-opposed walls provided with aligned apertures for the passage of an electron beam, a wall connecting said opposed walls It is noted that apparatus in accordance withour invention may take any form which effectively shields and having an aperture therein for the passage of electromagnetic wave energy, a waveguide coupled to said chamber through said last mentioned aperture and having an axis lying in a plane perpendicular to the direction of an electron beam passing through the aligned apertures in said spaced opposed walls, the axis of said guide extending along a curve of substantially and a dielectric Window hermetically sealed to said waveguide at the end thereof and shielded by means of a wall of said waveguide from a straight line exposure to an electron beam passing through said aligned apertures.

3. Apparatus for interaction with an electron beam and the transmission of high frequency electromagnetic energy comprising a chamber having spaced opposed walls provided with aligned apertures for the passage of an electron beam, a wall connecting said opposed walls and having an aperture therein for the passage of electromagnetic wave energy, a waveguide coupled to said chamber through said last mentioned aperture, a dielectric window hermetically sealed to said waveguide and shielded by means of a wall of said waveguide from straight line exposure to an electron beam passing through said aligned apertures, and a high energy electron impervious shield surrounding a substantial portion of said chamber and shielding said window from X-radiation.

References Cited in the file of this patent UNITED STATES PATENTS 1,902,474 Ungelenk et al. Mar, 21, 1933 1,956,396 Moran Apr. 24, 1934 2,063,329 Morrison Dec. 8, 1936 2,223,082 Van Mierlo Nov. 26, 1940 2,291,406 Paehr July 28, 1942 2,407,706 Shulman et' a1. Sept. 17, 1946 2,473,724 Oakress June 21, 1949 2,481,151 Powers Sept. 6, 1949' 2,735,034 McA'rthur Feb. 14, 1956 

